# Standard library header <bit> (C++20)

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This header is part of the numeric library.

### Types
endian (C++20) | indicates the endianness of scalar types (enum)
### Functions
bit_cast (C++20) | reinterpret the object representation of one type as that of another (function template)
byteswap (C++23) | reverses the bytes in the given integer value (function template)
has_single_bit (C++20) | checks if a number is an integral power of 2 (function template)
bit_ceil (C++20) | finds the smallest integral power of 2 not less than the given value (function template)
bit_floor (C++20) | finds the largest integral power of 2 not greater than the given value (function template)
bit_width (C++20) | finds the smallest number of bits needed to represent the given value (function template)
rotl (C++20) | computes the result of bitwise left-rotation (function template)
rotr (C++20) | computes the result of bitwise right-rotation (function template)
countl_zero (C++20) | counts the number of consecutive â0â bits, starting from the most significant bit (function template)
countl_one (C++20) | counts the number of consecutive 1 bits, starting from the most significant bit (function template)
countr_zero (C++20) | counts the number of consecutive â0â bits, starting from the least significant bit (function template)
countr_one (C++20) | counts the number of consecutive 1 bits, starting from the least significant bit (function template)
popcount (C++20) | counts the number of 1 bits in an unsigned integer (function template)

### Synopsis

    namespace std {
      // bit_cast
      template<class To, class From>
        constexpr To bit_cast(const From& from) noexcept;

      // byteswap
      template <class T>
        constexpr T byteswap(T value) noexcept;

      // integral powers of 2
      template<class T>
        constexpr bool has_single_bit(T x) noexcept;
      template<class T>
        constexpr T bit_ceil(T x);
      template<class T>
        constexpr T bit_floor(T x) noexcept;
      template<class T>
        constexpr int bit_width(T x) noexcept;

      // rotating
      template<class T>
        constexpr T rotl(T x, int s) noexcept;
      template<class T>
        constexpr T rotr(T x, int s) noexcept;

      // counting
      template<class T>
        constexpr int countl_zero(T x) noexcept;
      template<class T>
        constexpr int countl_one(T x) noexcept;
      template<class T>
        constexpr int countr_zero(T x) noexcept;
      template<class T>
        constexpr int countr_one(T x) noexcept;
      template<class T>
        constexpr int popcount(T x) noexcept;

      // endian
      enum class endian {
        little = /* see description */,
        big    = /* see description */,
        native = /* see description */
      };
    }

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